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Errors in forecasting load and renewable-based generation in restructured power systems mean that independent system operators (ISOs) must procure sufficient operating reserves to keep the real-time operation of the system reliable and secure. But when procured reserves turn out to be insufficient in real-time due to the lack of resource capacity or ramp capability, operators often set higher prices for reserves and energy to encourage more supply, and to motivate consumers to decrease usage or shift it to other times. This procedure, which is called scarcity or shortage pricing, is a core feature of U.S. electricity markets. It is receiving increased attention from market designers and stakeholders because scarcity will become more important for spot price formation in the future with the increased penetration of zero-marginal cost renewables, and the shrinking role of fuel costs in setting prices. Scarcity pricing is implemented in various ways by different ISOs. These differences have practical implications for the level of prices and incentives for investment, operations, and demand modification. In this paper, general approaches and specific calculation procedures for reserve and energy scarcity pricing practices and calculations across the seven ISO-based U.S. power markets are reviewed and compared. A consistent terminology is used to facilitate the comparison. Current scarcity pricing practices are grouped into three approaches: (1) imposing an adder after the spot market is run; (2) including stepwise demand curves within market clearing procedures for non-contingency reserve products (e.g., the novel flexiramp product), which tends to yield longer right tails for energy scarcity premium curves; and (3) having stepwise demand curves for traditional contingency reserve products only, which results in shorter right tails in energy scarcity curves. A generic numerical example is presented to highlight the large practical differences among the reserve scarcity pricing approaches and specific implementations. To further investigate factors that contribute the most to demand curves differences among ISOs, a sensitivity analysis is performed. This analysis shows that the largest source of differences among the curves is the scarcity prices assumed in the case of severe scarcity, while the number of steps used and whether flexiramp is considered also yields important differences in scarcity prices. As renewable penetration increases, it will become increasingly crucial to employ administrative demand curves so that spot prices more effectively motivate supply and demand adjustments exactly when and where they are needed. This study shows that the different assumptions yield very different scarcity premiums for reserves and energy, and are likely to provide divergent incentives for resources to respond to shortages. It is concluded that to promote market efficiency, a reserve shortage demand curve should have at least three features: inclusion of the marginal value of reserve products at each shortage level, consideration of the magnitude and probability of supply contingencies, and avoidance of abrupt price discontinuities that can cause excessively volatile market outcomes. • Explains principles and specific calculation procedures for reserve scarcity pricing practices across U.S. power markets. • Proposes a novel classification of sources of penalty values applied in the markets, highlighting their relative advantages. • Presents a generic numerical example to illustrate practical differences among the reserve scarcity pricing approaches. • Performs a sensitivity analysis to further investigate the most significant factors in differences among ISO demand curves. • Makes recommendations for defining demand curves for reserve scarcity pricing that accurately reflect the value of reserves. [ABSTRACT FROM AUTHOR]

Background: Advances in the prevention and treatment of atherosclerosis have been dramatic. The goal of this study was to evaluate any decline in the age adjusted incidence of acute non ST elevation myocardial infarction (NSTEMI) using a large database. Method: The Nationwide Inpatient Sample (NIS) database was utilized to calculate the age-adjusted rate for NSTEMI from 1988 to 2004 retrospectively. Specific ICD-9-CM codes for NSTEMI were used to compile the data. Patient demographic data was also analyzed from the database and adjusted for age. Results: The NIS database contained a total of 1 423 156 patients who had a diagnosis of NSTEMI from 1988 to 2004. The age-adjusted rate for all acute NSTEMI gradually increased from 1988 until 2000—26.21 per 100 000 (95% CI: 23.9–28.4) in 1988 and 92.6 per 100 000 (95% CI: 86.0–99.3, P <0.01 in 2000,). It remained unchanged from 2000 until 2004 (91.7 per 100 000 (95% CI: 85.3–98.0). This trend was similar across different race and gender. Conclusion: The increasing incidence of NSTEMI from 1988 until year 2000 has suddenly stabilized by the year 2000. The cause of this finding is unknown. It could be related to the recent adaptation of troponin testing or recent advancement in the prevention and treatment of atherosclerosis. [ABSTRACT FROM AUTHOR]

Background & Aims: In recent years, there have been many advances in the primary and secondary prophylaxis of variceal bleeding. The aim of this study was to evaluate nationwide trends in the hospitalization rate of bleeding esophageal varices in the advent of these new modalities. In addition, our aims were to study the incidence trends of nonbleeding esophageal varices over the past 2 decades while studying hospitalization rates for cirrhosis over the same study period. Methods: The Nationwide Inpatient Sample database was used for inpatient data analysis (1988–2002) and the State Ambulatory Surgery Database was used for outpatient analysis. Patients discharged with International Classification of Diseases, ninth revision, Clinical Modification discharge diagnoses related to esophageal varices were included. Results: The hospitalization rate of bleeding varices increased 13.7% from 10.9 per 100,000 in the 1988 to 1990 period to 12.4 per 100,000 in the 1994 to 1996 period (P < .01), and then decreased 14.5% to 10.6 per 100,000 in the 2000 to 2002 period (P < .01). In-hospital nonbleeding varices increased 55% from 6.0 to 9.3 per 100,000 from the 1988 to 1990 period to the 2000 to 2002 period (P < .01). Outpatient nonbleeding esophageal varices increased 20% from 5.5 to 6.6 per 100,000 from 1997 to 2003. Conclusions: The hospitalization rate for bleeding esophageal varices has been on the decline in recent years and may be a reflection of the advances in primary and secondary prophylaxis. The incidence rate of nonbleeding esophageal varices is increasing and likely is owing to the increasing burden of portal hypertensive liver disease in the nation. [Copyright &y& Elsevier]

OBJECTIVES: To evaluate nationwide trends in the utilization of endoscopic retrograde cholangiopancreatography (ERCP) in relation to the advent of noninvasive methods of visualizing the biliary and pancreatic tree. METHODS: Retrospective cohort study. The Nationwide Inpatient Sample (NIS) database was used to calculate the age-adjusted rate for ERCPs performed from 1988 to 2002. The State Ambulatory Surgery Database (SASD) was used to evaluate trends in outpatient ERCPs from 1997 to 2003. Linear Poisson multivariate regression model was used to control for variations in age, gender, and ethnicity among the overall patient population. RESULTS: The NIS database contained 402,343 patients who had an ERCP performed from 1988 to 2002. The mean age for these patients was 60.21 ± 19.56 yr old. From 1988 to 1996; the age-adjusted rate for ERCPs increased by nearly threefold, from 25.66 per 100,000 in 1988 to 74.95 in 1996. The rate of 74.95 in 1996 declined to a rate of 59.70 by the year 2002. The rates of diagnostic ERCPs in men and women were 26.76 and 31.58 per 100,000 in 1988–1990, respectively. This rate then increased to 35.66 and 43.18 per 100,000 in 1994–1996, which then declined to 29.01 and 29.06 in 2000–2002. The age-adjusted rate for therapeutic ERCPs in men and women was 13.74 and 15.61 per 100,000 in 1988–1990, respectively, which continued to increase throughout the time span to 38.76 and 43.75 in 2000–2002. The SASD revealed a continual decline in outpatient ERCPs from 25.45 per 100,000 in 1997 down to 16.17 per 100,000 in the year 2003. CONCLUSION: The utilization of ERCP dramatically increased from 1988 to 1996; however, since the advent of noninvasive diagnostic techniques such as endoscopic ultrasound (EUS) and magnetic resonance cholangiopancreatography (MRCP), there has been a steady decline in the utilization of diagnostic ERCPs from 1996 to 2002. [ABSTRACT FROM AUTHOR]

Objective: This study examined nationwide trends in use of coronary artery bypass grafting between 1988 and 2004. Methods: The Nationwide Inpatient Sample database was used to calculate age-adjusted rate of coronary artery bypass grafting from 1988 to 2004. Specific International Classification of Diseases, Ninth Revision, Clinical Modification codes for coronary artery bypass grafting were used to compile data. Patient demographic data were also analyzed. Results: The database recorded 1,145,285 patients older than 40 years who underwent coronary artery bypass grafting from 1988 to 2004. Mean age was 60.21 ± 10.55 years. Male patients underwent coronary artery bypass grafting more than twice as frequently as female patients (70.6% vs 29.4%). From 1988, total age-adjusted rate gradually increased for 10 years until 1997 (79.29 per 100,000 with 95% confidence interval 70.88–87.71 per 100,000 in 1988, 131.31 per 100,000 with 95% confidence interval 119.02–143.59 per 100,000 in 1997, P < .01), with ensuing rapid decline to nearly the lowest level at end of study in 2004 (83.01 per 100,000 with 95% confidence interval 75.68–90.33 per 100,000, P < .01). Although trends were similar across ethnicity and sex, female and ethnic minority patients had lower rates of bypass surgery than did male and white patients. Conclusions: Use of coronary artery bypass grafting has decreased dramatically in recent years, with even lower use among female and ethnic minority patients. This decline may be related to significant advances in percutaneous coronary interventions and improved medical treatment of atherosclerosis in the past 10 years. [Copyright &y& Elsevier]

Background: Atrial fibrillation (AF) is common in patients presenting with myocardial infarction (MI). Percutaneous coronary intervention (PCI) has been shown to improve cardiovascular outcomes in MI. However, outcomes of PCI in AF patients presenting with MI remains largely unknown.Methods: We analyzed the Nationwide Inpatient Sample (NIS) database to calculate the age adjusted mortality rate for PCI in AF patients presenting with MI between 2002 and 2011, in adults over 40 years of age. This was then compared to the mortality rate for PCI in non-AF patients with MI. Specific ICD-9-CM codes were used to identify patients and outcomes.Results: Of 3,226,405 PCIs done during the study period, 472,609 (14.6%) PCIs were done on AF patients of which 137,870 PCIs were for MI. About 60% of these patients were male. Patients with AF were older (71.3 ± 10.6 years). Overall the number of PCIs shows a declining trend from 2002 to 2011, but for MI patients the number of PCIs appears stable over the years. The age adjusted in-hospital mortality following PCI in MI was significantly higher in AF group compared to the non-AF group (190.24 ± 17.21vs 109.08 ± 5.89 per 100,000; P < 0.01). This trend was seen during the entire study period.Conclusions: AF is prevalent in MI patients undergoing PCI. AF is associated with increased mortality following PCI for acute MI. AF is not a benign arrhythmia in MI patients and close attention is warranted in these patients to improve mortality. [ABSTRACT FROM AUTHOR]

Background: Atrial fibrillation (AF) is the most common cardiac arrhythmia with a prevalence of 15% of patients over 80 years. Coronary artery disease co-exists in 20-30% of patients with atrial fibrillation. The need for triple anticoagulation therapy makes the management of these patients challenging following PCI.Methods: Nationwide inpatient sample which is a set of longitudinal hospital inpatient databases was used to evaluate the outcome of patients with AF who underwent PCI. All patients undergoing PCI between 2002 and 2011 were included in the study. Specific ICD-9-CM codes were used to identify the study patients and their outcomes.Results: There were 3,226,405 PCIs during the time period of the study of which 472,609 (14.6%) patients had AF. AF patients were older and predominantly male (60%). The number of PCIs had a declining trend from 2002 to 2011. Age adjusted inpatient mortality was significantly higher in PCI AF group compared to the PCI non-AF group (100.82 ± 9.03 vs 54.07 ± 8.96 per 100,000; P < 0.01). Post PCI predictors of mortality were AF (OR 1.56, CI 1.53-1.59), CKD (OR 1.41, CI 1.37-1.46), PAD (OR 1.20, CI 1.15-1.24), acute myocardial infarction (OR 2.42 CI 2.37-2.46 and cardiogenic shock (OR 13.92 CI 13.60-14.24) P < 0.001.Conclusion: AF is common in patients undergoing PCI and those AF patients have a higher age-adjusted all cause inpatient mortality. There is a decline in total number of PCIs over time in US. Atrial fibrillation, chronic kidney disease, peripheral artery disease, MI and cardiogenic shock were associated with increased mortality following PCI. [ABSTRACT FROM AUTHOR]

Background Recent improvement in the care of patients with myocardial infarction should lead to better outcome. The goal of this study was to evaluate the incidence of all cause cardiogenic shock (CS) and CS occurring in the setting of ST elevation myocardial infarction (STEMI) in the United States. Method The Nationwide Inpatient Sample (NIS) database was utilized to calculate the age-adjusted incident rate of CS from 1996 to 2006 based on ICD-9 coding in the setting of STEMI. Furthermore, we evaluated this trend based on race and gender. Results A total population of 52,784,917 patients was available between 1996 and 2006. We found that the incidence of all cause CS has not changed over time. However, in the setting of STEMI, CS has been declining slowly over the last 10 years. The age-adjusted rate for CS was 4.3 per 100,000 in 1996 which remained steady with an incidence of 3.1 per 100.000 in 2006 (p < 0.01). This decline was persistent across different race or gender. However, African Americans and female gender had persistently lower rate of CS. Conclusion Advancement in the treatment of acute STEMI has led to gradual reduction in the incidence of STEMI related cardiogenic shock irrespective of ethnicities or gender suggesting improving outcome of patients presenting with STEMI in recent years. [ABSTRACT FROM AUTHOR]

Treatment of acute ST-segment elevation myocardial infarction (STEMI) has dramatically changed over the past 2 decades. The goal of this study was to determine trends in the mortality of patients with acute STEMIs in the United States over a 16-year period (1988 to 2004) on the basis of gender, race, infarct location, and co-morbidities. The Nationwide Inpatient Sample database was used to analyze the age-adjusted mortality rates for STEMI from 1988 to 2004 for inpatients age >40. International Classification of Diseases, Ninth Revision, Clinical Modification codes consistent with acute STEMI were used. The Nationwide Inpatient Sample database contained a total of 1,316,216 patients who had diagnoses of acute STEMIs from 1988 to 2004. The mean age of these patients was 66.92 ± 12.82 years. A total of 163,915 hospital deaths occurred during the study period. From 1988, the age-adjusted mortality rate decreased gradually for all acute STEMIs for the entire study period (in 1988, 406.86 per 100,000, 95% confidence interval 110.25 to 703.49; in 2004, 286.02 per 100,000, 95% confidence interval 45.21 to 526.84). Furthermore, unadjusted mortality decreased from 15% in 1988 to 10% in 2004 (p <0.01). This decrease was similar between the genders, among most ethnicities, and in patients with diabetes and those with congestive heart failure. However, women and African Americans had higher rates of acute STEMI–related mortality compared to men and Caucasians over the years studied. In conclusion, age-adjusted mortality from acute STEMIs has significantly decreased over the past 16 years, with persistent higher mortality rates in women and African Americans the study period. [Copyright &y& Elsevier]

Advances in the management of atherosclerosis risk factors have been dramatic in the previous 10 years. The goal of this study was to evaluate any decrease in age-adjusted incidence of acute ST-elevation myocardial infarction (STEMI) in a very large database of inpatient admissions from 1988 to 2004. The Nationwide Inpatient Sample database was used to calculate the age-adjusted rate for STEMI from 1988 to 2004 retrospectively. Specific International Classification of Diseases, Ninth Revision, codes for MIs consistent with STEMI were used. Patient demographic data were also analyzed and adjusted for age. The Nationwide Inpatient Sample database contained 1,352,574 patients >40 years of age who had a diagnosis of STEMI from 1988 to 2004. Mean age for these patients was 66.06 ± 13.69 years. Men had almost 2 times the age-adjusted STEMI rate as women (men 62.4%, women 37.6%). From 1988 the age-adjusted rate for all acute STEMIs remained steady for 8 years (108.3 per 100,000, 95% confidence interval [CI] 99.0 to 117.5, in 1988 and 102.5 per 100,000, 95% CI 94.7 to 110.4, in 1996). However, from 1996 onward, the age-adjusted incidence of STEMI steadily decreased to 1/2 the incidence of the previous 8 years (50.0 per 100.000, 95% CI 46.5 to 53.5, by 2004, p <0.01). This decrease was similar across various races and genders. In conclusion, the incidence of STEMI was stable from 1988 to 1996, with a steady linear decrease to 1/2 by 2004. The cause of the steady decrease in STEMI rate most likely reflects the advancement in management of patients with atherosclerosis. [Copyright &y& Elsevier]